Sheet feeding apparatus

Abstract

A belt type separator contacts a stack to feed a sheet to a retard nip formed between the belt and a retard member. The belt is supported by a first pulley downstream of the stack and a second pulley adjacent the stack which is pivotable relative to the first pulley. Frictional resistance encountered by the belt at the nip will cause the normal force with which the belt bears against the stack to increase. Oppositely skewed rolls are used to tension sheets fed to a sheet aligning abutment. When the separator is positioned below the stack, a pivotable lever may be used to hold the stack against the separator. The pressing effect of the lever may be overridden upon an increase of the force with which the separator engages the stack.

What is claimed is: 
     
       1. Sheet feeding apparatus for feeding individual sheets from a stack of said sheets comprising: friction means for feeding said sheets from said stack, said feeding means engaging said stack with a first normal force;   friction retard means engaging said feeding means to form a nip therebetween for passage of said sheets, said feeding means encountering a frictional resistance at said nip; and   means responsive to said frictional resistance encountered by said feeding means at said nip for increasing said first normal force to a second normal force greater than said first force when a sheet is being fed by said feeding means.   
     
     
       2. An apparatus as in claim 1, wherein said second normal force increases or decreases as said frictional resistance increases or decreases respectively, whereby said normal force increasing means is self-compensating. 
     
     
       3. An apparatus as in claim 2, wherein said feeding means and said retard means are pivotally mounted about a given pivot axis and further including drive means for driving said feeding means, said drive means being mounted for rotation about said axis in a given direction, said direction being selected to cause said feeding means to pivot against said stack during feeding. 
     
     
       4. An apparatus as in claim 3, further including counterbalance means for counterbalancing a substantial portion of the weight of said feeding means whereby said first normal force comprises the weight of said feeding means as counter-balanced by said counterbalance means. 
     
     
       5. An apparatus as in claim 3, wherein said feeding means comprises a belt feeder engaging the leading edge of said stack and said retard means has a finitely curved frictional retard surface deformably engaging said feed belt in an unsupported region to provide a sheet queing throat. 
     
     
       6. An apparatus as in claim 5, further including registration means for intercepting and registering said sheet fed by said feeding means, said registration means being positioned so that a sheet upon being intercepted is still held within the nip of said feeding means, said registration means comprising means for transporting said sheet following registration, said transport means engaging said sheet with sufficient force to overcome the drag of said feeding means, said feeding means continuously engaging said stack, and means for disengaging said input drive means from said feeding means for reducing said normal force to said first normal force. 
     
     
       7. An apparatus as in claim 6, wherein said disengaging means is operative when a sheet is being transported by said transport means, whereby the drag exerted by said feeding means on said sheet during said transport is reduced. 
     
     
       8. An apparatus as in claim 1, wherein said first normal force is relatively low and is selected within the range of from 0 up to a force sufficient to maintain frictional contact between said feed means and said stack, and wherein said responsive means is adapted to increase said first force to a second normal force substantially higher than said first force. 
     
     
       9. A reproducing apparatus including: an imaging means for forming an image on a copy sheet;   friction means for feeding said sheets from a stack thereof, said feeding means engaging said stack with a first normal force;   friction retard means engaging said feeding means to form a nip therebetween for passage of said sheet, said feeding means encountering a frictional resistance at said nip; and   means responsive to said frictional resistance encountered by said feeding means at said nip for increasing said first normal force to a second normal force greater than said first force when a sheet is being fed by said feeding means.   
     
     
       10. An apparatus as in claim 9, wherein said second normal force increases or decreases as said frictional resistance increases or decreases respectively, whereby said normal force increasing means is self-compensating. 
     
     
       11. An apparatus as in claim 10, wherein said feeding means and said retard means are pivotally mounted about a given pivot axis and further including drive means for driving said feeding means, said drive means being mounted for rotation about said axis in a given direction, said direction being selected to cause said feeding means to pivot against said stack during feeding. 
     
     
       12. An apparatus as in claim 11, further including counterbalance means for counterbalancing a substantial portion of the weight of said feeding means whereby said first normal force comprises the weight of said feeding means as counter-balanced by said counterbalance means. 
     
     
       13. An apparatus as in claim 11, wherein said feeding means comprises a belt feeder engaging the leading edge of said stack and said retard means has a finitely curved frictional retard surface deformably engaging said feed belt in an unsupported region to provide a sheet queing throat. 
     
     
       14. An apparatus as in claim 13, further including registration means for intercepting and registering said sheet fed by said feeding means, said registration means being positioned so that a sheet upon being intercepted is still held within the nip of said feeding means, said registration means comprising means for transporting said sheet following registration, said transport means engaging said sheet with sufficient force to overcome the drag of said feeding means, said feeding means continuously engaging said stack, and means for disengaging said input drive means from said feeding means for reducing said normal force to said first normal force. 
     
     
       15. An apparatus as in claim 14, wherein said reproducing apparatus comprises an electrostatographic reproducing machine wherein said imaging means includes: an imaging member, means for forming an electrostatic image upon said imaging member, means for developing said electrostatic image and means for transferring said developed image from said imaging member to said sheet. 
     
     
       16. An apparatus as in claim 14, wherein said disengaging means is operative when a sheet is being transported by said transport means, whereby the drag exerted by said feeding means on said sheet during said transport is reduced. 
     
     
       17. An apparatus as in claim 9, wherein said first normal force is relatively low and is selected within the range of from 0 up to a force sufficient to maintain frictional contact between said feed means and said stack, and wherein said responsive means is adapted to increase said first force to a second normal force substantially higher than said first force. 
     
     
       18. In a reproducing apparatus including means for forming an image on a copy sheet and means for transporting said sheet in a given direction along a sheet feed path to said imaging means, the improvement wherein said apparatus further includes: means for placing said sheet in tension in a direction transverse to said given direction as said sheet is transported to said imaging means, said tensioning means comprising first and second toed out rolls each defining an axis of rotation, said axis of said first roll being canted with respect to said given direction, and said axis of said second roll being generally oppositely canted with respect to said given direction;   a common shaft for supporting said toed out rolls for rotation thereabout;   at least one middle roll supported about said shaft between said toed out rolls with the axis of rotation of said middle roll being normal to said given direction;   means for registering a sheet with respect to said imaging means, said registration means including said rolls and stop means for intercepting a lead edge of said sheet, said stop means being movable in and out of sheet blocking relationship in said sheet feed path, and   pinch rolls for engaging said first and second rolls to form a nip for advancement of sheets therebetween, said pinch roll being coaxially aligned about an axis positioned normal to said given direction.   
     
     
       19. An apparatus as in claim 18, wherein said reproducing apparatus comprises an electrostatographic reproducing machine wherein said imaging means includes an imaging member, means for forming an electrostatic image upon said imaging member, means for developing said electrostatic image and means for transferring said developed image from said imaging member to said sheet. 
     
     
       20. An apparatus as in claim 18, wherein said first and second rolls are canted to the same extent with respect to said given direction. 
     
     
       21. An apparatus as in claim 18, wherein said stop means is positionable just ahead of the nip of said rolls for intercepting the lead edge of said sheet, said stop means being movable out of said sheet feed path for directing said sheet into said nip. 
     
     
       22. A sheet feeding apparatus for feeding individual sheets from the bottom of a stack of said sheets comprising: friction feeding means for feeding said sheets from the bottom of said stack, said feeding means engaging said stack with a given normal force;   adjustable stop means engaging the top of said stack for restraining said stack against said feeding means;   override means for disengaging said stop means from said stack upon the application of a force of a desired level greater than said given force;   said stop means comprising a lever which is pivotally mounted at one end for movement of the other end toward and away from said stack, and said override means comprising a one way clutch connected to said lever.   
     
     
       23. A sheet feeding apparatus for feeding individual sheets from the bottom of a stack of said sheets comprising; friction feeding means for feeding said sheets from the bottom of said stack, said feeding means engaging said stack with a given normal force;   friction retard means engaging said feeding means to form a nip therebetween for passage of said sheets;   means responsive to a frictional resistance encountered by said feeding means at said nip for increasing said given normal force to a second normal force when a sheet is being fed by said feeding means;   adjustable stop means engaging the top of said stack for restraining said stack against said feeding means; and   override means for disengaging said stop means from said stack upon the application of a force of a desired level greater than said given force.   
     
     
       24. An apparatus as in claim 23, wherein said second normal force increases or decreases as said frictional resistance increases or decreases respectively, whereby said normal force increasing means is self-compensating. 
     
     
       25. An apparatus as in claim 24, wherein said feeding means and said retard means are pivotally mounted about a given pivot axis and further including drive means for driving said feeding means, said drive means being mounted for rotation about said axis in a given direction, said direction being selected to cause said feeding means to pivot against said stack during feeding. 
     
     
       26. An apparatus as in claim 25, wherein said feeding means comprises a belt feeder engaging the leading edge of said stack and said retard means has a finitely curved frictional retard surface deformably engaging said feed belt in an unsupported region to provide a sheet queing throat. 
     
     
       27. An apparatus as in claim 26, further including registration means for intercepting and registering said sheet fed by said feeding means, said registration means being positioned so that a sheet upon being intercepted is still held within the nip of said feeding means, said registration means comprising means for transporting said sheet following registration, said transport means engaging said sheet with sufficient force to overcome the drag of said feeding means, said feeding means continuously engaging said stack, and means for disengaging said input drive means from said feeding means for reducing said normal force to said first normal force. 
     
     
       28. An apparatus as in claim 27, wherein said stop means comprises a lever which is pivotally mounted at one end for movement of the other end toward and away from said stack and wherein said override means comprises a one way clutch connected to said lever. 
     
     
       29. An apparatus as in claim 28, wherein said transporting means transports said sheet to a means for forming an image on said sheet. 
     
     
       30. An apparatus as in claim 28, wherein said apparatus comprises part of an electrostatic reproducing apparatus and wherein said imaging means includes: an imaging member, means for forming an electrostatic image upon said imaging member, means for developing said electrostatic image and means for transferring said developed image from said imaging member to said sheet. 
     
     
       31. An apparatus as in claim 30, wherein said transport means transports said sheets in a given direction along a sheet feed path and wherein said apparatus further includes: means for placing said sheet in tension in a direction transverse to said given direction as said sheet is transported to said imaging means, said tensioning means including a first means for imparting a force to said sheet directed transversely of said given direction in a first outwardly direction, and second means spaced from said first means for imparting a force to said sheet directed transversely of said given direction in a second outwardly direction, said second outwardly direction generally opposing said first outwardly direction so as to place said sheet under tension between said first means and said second means, and first means and said second means comprising first and second rolls, respectively.   
     
     
       32. An apparatus as in claim 31, wherein the axis of rotation of said first roll is canted with respect to said given direction and wherein the axis of rotation of said second roll is generally oppositely canted with respect to said given direction, whereby said rolls are toed-out with respect to each other. 
     
     
       33. An apparatus as in claim 30, wherein said feeding means and said transporting means are spaced sufficiently close together so that they operate simultaneously upon said sheet during a given time interval, and wherein said apparatus further includes: means for forming a bend in said sheet during said time interval which is transverse to said given direction, said bending means being positioned in said sheet feed path between said feeding means and said transport means, whereby a more uniform force distribution is created in said sheet between said bend and said transport means.   
     
     
       34. An apparatus as in claim 33, wherein said feed means and said retard means engage said sheet over a limited portion of its transverse width, said apparatus further including, means for guiding the remaining portion of the width of said sheet through a curved path corresponding substantially to the curve of said nip.   
     
     
       35. A sheet feeding apparatus for feeding individual sheets from a stack of said sheets comprising: friction means for feeding said sheets from said stack, said feeding means being mounted for movement toward and away from said stack;   friction retard means engaging said feeding means to form a nip therebetween for passage of said sheets, said feeding means encountering a frictional resistance at said nip; and   means responsive to said frictional resistance encountered by said feeding means at said nip during feeding for forcing said feeding means against said stack with a given normal force.   
     
     
       36. An apparatus as in claim 35, wherein said given normal force increases or decreases as said frictional resistance increases or decreases respectively, whereby said forcing means is self-compensating. 
     
     
       37. An apparatus as in claim 36, wherein said feeding means and said retard means are pivotally mounted about a given pivot axis and further including drive means for driving said feeding means, said drive means being mounted for rotation about said axis in a given direction, said direction being selected to cause said feeding means to pivot against said stack during feeding. 
     
     
       38. An apparatus as in claim 37, wherein said friction retard means continuously engages said feed means and, wherein when said feeding means is not feeding, it does not engage said stack. 
     
     
       39. An apparatus as in claim 38, wherein said feeding means comprises a belt feeder engaging the leading edge of said stack and said retard means has a finitely curved frictional retard surface deformably engaging said feed belt in an unsupported region to provide a sheet queing throat. 
     
     
       40. An apparatus as in claim 39, further including registration means for intercepting and registering said sheet fed by said feeding means, said registration means being positioned so that a sheet upon being intercepted is still held within the nip of said feeding means, said registration means comprising means for transporting said sheet following registration, said transport means engaging said sheet with sufficient force to overcome the drag of said nip of said feeding means, and means for disengaging said input drive means from said feeding means for reducing said given force. 
     
     
       41. An apparatus as in claim 40, wherein said feeding means feeds from the bottom of the stack. 
     
     
       42. An apparatus as in claim 41, wherein said disengaging means is arranged to be operative when a sheet is being transported by said transport means, whereby the drag exerted by said feeding means on said sheet during transport is reduced.